The present invention relates to an image reading apparatus, and more specifically, it relates to an image reading apparatus for reading image information by scanning an original divided into a plurality of regions along a main scanning direction.
An image reading apparatus of a plane scanning type such as a scanner which scans an original divided into a plurality of regions along the main scanning direction to read image information. The image reading apparatus comprises an original retainer for retaining an original, a light source for irradiating the original with light, a plurality of CCDs (an example of a solid-state imaging device) which are arranged along the main scanning direction and having a corresponding array of pixels, and a plurality of lenses arranged along the main scanning direction for forming an image of the original on the solid-state imaging devices and which correspond respectively to the plurality of regions.
According to the above image reading apparatus, displacement of the original in the direction of its thickness (the direction of an optic axis) causes the image information to overlap or gap at a boundary of the regions to be read. In order to prevent the above problems, prior art teaches: use of a field lens for increasing a focal length, disposing it between lenses for forming an image of the original (Japanese Patent Publication 12062/1992); reduction of an angle of view on the boundary side of a region of adjacent regions (Japanese Patent Laid Open No. 11156/1983); or the provision of a displacement detecting means for detecting the direction of displacement of the original in the direction of the optic axis and the amount thereof (Japanese Patent Laid Open No. 109862/1991).
Conventional structures which provide for a field lens, complicates the optical system because the number of lens is increased. Consequently, the apparatus becomes expensive and adjustment of the optical system becomes complicated. Further, conventional structures in which the angle of view on the boundary side of the region is reduced also require a complicated adjustment because it is necessary to adjust positions of the CCDs in the main scanning direction in order to adjust the angle of view. In addition, conventional structures which provide a displacement detecting means, a displacement sensor such as a laser displacement sensor is necessary. The sensor makes the apparatus expensive and its adjustment is complicated.